The present invention relates to a method and system for temperature calibration of a thermogravimetric analyzer.
Thermogravimetric equipments are used in many industrial and scientific environments to analyze the characteristics of a broad range of materials either solid or liquid. One of the main uses of a thermogravimetric analyzer is to measure the mass variations caused by sensible changes of temperature in a material specimen. Thermogravimetric analyzers must be able to continuously measuring the mass of a specimen in a controlled atmosphere and in a controlled environment over a selected period of time.
FIG. 1 shows schematically the structure and the functioning of a thermogravimetric analyzer. The specimen to be analyzed is placed on a crucible 101 on a plate of a very sensitive (e.g. sensitive to 5 xcexcg) electronic microbalance 103 inside a furnace 105 having an inert atmosphere (e.g. purified grade N2 or other inert gas). The temperature inside the furnace 105 is then continuously varied by means of a temperature programmer, which provides a linear rate of rise; e.g. the temperature may be incremented by 10xc2x0 C./min from 25xc2x0 C. to 800xc2x0 C. The variations of temperature are measured by a thermocouple 107 and the variations in the specimen mass are measured by the microbalance 103. These measurements are usually executed by a computer 109 for obtaining indications of the change of mass in relation to temperature changes.
This mass change curve in thermogravimetry is normally influenced by many features which are characteristic of the thermogravimetric analyzer, e.g. the shape and composition of the specimen holder, the design of the furnace or the precision of the measuring sensors. These differences make it difficult to obtain absolute results and to compare experiments made with different equipment. For the above reasons a calibration of the thermogravimetric analyzer must be done.
According to the xe2x80x9cStandard Practice for Calibration of Temperature Scale for Thermogravimetryxe2x80x9d E1582-93 approved on Nov. 15, 1993 by the American Society for Testing and Materials (ASTM) and published January 1994, this calibration can be done either by measurement of a melting or a magnetic (Curie Point) transition temperature from the standard reference temperature. The above referenced Standard Practice describes three procedures for temperature calibration of Thermogravimetric analysers: two using melting point standards, one using magnetic transition standards for calibration.
Curie point is defined as the temperature at which ferromagnetic properties disappear and it occurs within a range of temperatures rather than at a precise temperature point. On the contrary, the melting point of metals is a well established physical property which occurs at precise temperatures. For this reason, the method based on melting point of metals (standard materials) is usually preferred to set a temperature calibration scale.
However the known methods using the melting points usually require complex manual operation for each single test: a new operation is required for each metal sample used as calibration point. This is not only time consuming, but could also cause inaccurate results due to different operator""s experience.
It is an object of the present invention to alleviate the above drawbacks of the prior art.
The object of the present invention has been achieved by providing according to a first aspect of the invention an apparatus for temperature calibration of a thermogravimetric analyzer comprising:
a crucible;
at least one weight;
a metal foil corresponding to the at least one weight and having a melting point, said metal foil supporting said at least one weight in said crucible, wherein when said melting point is reached, said metal foil is not able to support said at least one weight causing the dropping of said at least one weight in the crucible.
According to a second aspect of the invention there is provided a thermogravimetric analyzer and calibration apparatus comprising:
a furnace;
a microbalance for measuring changes of mass inside the furnace;
a temperature controller to control the themperature inside the furnace;
a recording apparatus to record changes of mass inside the furnace in relation to temperature changes; and
an apparatus for temperature calibration of the thermogravimetric analyzer placed in the furnace comprising:
a crucible placed on said microbalance;
at least one weight;
a metal foil corresponding to said at least one weight and having a melting point, said metal foil supporting said at least one weight in said crucible, wherein when said melting point is reached, said metal foil is not able to support said at least one weight causing the dropping of the weight in the crucible.
According to a third aspect of the invention, there is provided a method for temperature calibration of a thermogravimetric analyzer including a furnace, a microbalance for measuring changes of mass inside the furnace, a temperature controller to control temperature inside the furnace and a recording apparatus, the method comprising the steps of:
suspending within the furnace at least one weight by a corresponding metal foil having a melting point above which the metal foil is not able to support the at least one weight;
increasing the temperature inside the furnace until at least the melting point of the foil is reached causing the dropping of the at least one weight;
detecting, by means of the microbalance, the dropping of the at least one weight and recording the temperature at the moment of said detecting.
According to a fourth aspect of the invention there is provided a method for temperature calibration of a thermogravimetric analyzer including a furnace, a microbalance for measuring changes of mass inside the furnace, a temperature controller to control temperature inside the furnace and a recording apparatus, the method comprising the steps of:
suspending within the furnace a plurality of weights by a corresponding plurality of metal foils, each of the plurality of metal foils having a different melting point above which the metal foil is not able to support its corresponding weight;
increasing the temperature inside the furnace until at least the lower of the melting points of the foils is reached causing the dropping of its corresponding weight, the plurality of metal foils being arranged so that when a weight drops it does not hit a metal foil having a higher melting point;
detecting, by means of the microbalance, the dropping of the corresponding weight and recording the temperature at the moment of said detecting.